(1) Field of the Invention
The present invention relates to a semiconductor device, and specifically relates to a semiconductor memory including hierarchized bit lines.
(2) Description of Related Art
The art related to the present invention includes a semiconductor memory device disclosed in Japanese Patent Laid-Open No. 2008-71384. In this semiconductor memory device, a plurality of bit lines are provided for one read/write amplifier, and a bit line selected from those bit lines is electrically connected to the read/write amplifier.
The present inventors have found that semiconductor memory devices such as disclosed in Japanese Patent Laid-Open No. 2008-71384 cause the following problems.
When a non-selected bit line adjacent to a selected bit line is in a floating state, noise is introduced to the floating non-selected bit line via word lines or the substrate, and the noise introduced to the non-selected bit line may affect the selected bit line. In order to reduce the effect of such noise, normally, non-selected bit lines are clamped (fixed) to a reference potential (normally, ground potential).
For clamping means, a technique in which, for example, an NMOS transistor is provided between each bit line and a reference potential, and the on/off of this NMOS transistor is controlled using the inverted level of a corresponding bit line selection signal may be employed. However, such fixing means requires provision of an inverter for inverting the level of a bit line selection signal to each bit line, resulting in an increase in the number of components constituting the circuit.